By connecting FORCEON to INVALID, the device shuts

down when no valid receiver level and no receiver or

transmitter edge is detected for 30sec. It wakes up

when a valid receiver level or receiver or transmitter

edge is detected.

By connecting FORCEON and FORCEOFF to INVALID,

the device shuts down when no valid receiver level is

detected and wakes up when a valid receiver level is

detected.

A system with AutoShutdown Plus may need time to

wake up. Figure 4 shows a circuit that forces the

transmitters on for 100ms, allowing enough time

for another system to realize that the MAX3233E/

MAX3235E is awake. If another system outputs valid

RS-232 signal transitions within that time, the RS-232

ports on both systems remain enabled.

Software-Controlled Shutdown

If direct software control is desired, use INVALID to

indicate DTR or Ring Indicator signal. Tie FORCEOFF

and FORCEON together to bypass the AutoShutdown

Plus so the line acts like a SHDN input.

±15kV ESD Protection

As with all Maxim devices, ESD-protection structures are

incorporated on all pins to protect against electrostatic

discharges encountered during handling and assembly.

The driver outputs and receiver inputs have extra pro-

tection against static electricity. Maxim’s engineers have

developed state-of-the-art structures to protect these

pins against ESD of ±15kV without damage. The ESD

structures withstand high ESD in all states: normal

operation, shutdown, and powered down. After an ESD

±15kV ESD-Protected, 1µA, 250kbps, 3.3V/5V, Dual

RS-232 Transceivers with Internal Capacitors

8

_______________________________________________________________________________________

Table 2. INVALID Truth Table

Low

No

High

Yes

INVALID OUTPUT

RS-232 SIGNAL

PRESENT AT ANY

RECEIVER INPUT

-2.7

-0.3

+2.7

+0.3

0

INDETERMINATE

INVALID HIGH

INVALID LOW

INVALID HIGH

INDETERMINATE

Figure 3a. Receiver Positive/Negative Thresholds for INVALID

0

V+

V-

0

INVALID

OUTPUT

TRANSMITTER

INPUTS

RECEIVER

INPUTS

}

INVALID

REGION

TRANSMITTER

OUTPUTS

Figure 3b. AutoShutdown Plus, INVALID, and READY Timing Diagram